When it comes to nitrogen and soil, the rains giveth and the rains taketh away. Nitrogen is the most expensive fertilizer a row crop farmer uses, and one of the most important, and it helps the bottom line to know when it’s there and when it’s not before applying it.
Jake Mowrer, a Texas AgriLife Extension soil specialist, told farmers at last month’s Stiles Farm Field Day that when it rains, and as the soil is absorbing water, a lot of the nitrogen migrates deeper into the soil. It doesn’t show up in a standard soil test, which samples the first six inches or so of soil, but it’s often there, just waiting for the plant to utilize it.
The deeper the root system, the deeper the plant can access nitrogen and other nutrients. Cotton roots extend about three feet deep. Milo and sorghum roots can go as deep as six feet and also have a more lateral root system.
“If you don’t meet your yield goal one year, you might still have a substantial amount of nitrogen for the next year,” Mowrer said.
The deeper testing may require a hydraulic probe instead of a simple auger, but Mowrer cited Texas A&M research that calculated savings of $20 to $30 an acre by utilizing deep nitrogen.
“You pay an extra $10 for the deep test, but $20 to $30 per acre is a huge savings for a $10 investment,” Mowrer said.
But not all the nitrogen goes deep. Rains of historic duration and intensity, like the ones much of the state experienced this year, can also cause fields to lose nitrogen.
Ronnie Schnell, a cropping specialist with Texas AgriLife Extension, said the spring deluges left a lot of standing water in fields and caused everybody to lose nitrogen this year, whether from leeching or runoff. The soil and the plant like rain, but when the plant’s saturated for an extended period of time, the plants begin to take in oxygen in lieu of nitrogen, which escapes into the air.
Schnell said the question farmers face now is whether or not to put out “rescue” nitrogen this late in the growing season. But how late is too late? Some of the new varieties allow farmers to apply some late nitrogen to corn that’s close to tasseling, Schnell said.
“You might have a 10 percent yield loss, but that’s better than the 30 percent you’ll get if you don’t put it out,” he said.
Schnell showed the producers corn stalks of varying heights to help them determine if a plant is redeemable. He said severely-stressed plants with small leaves might not be worth saving.
“But if the plant is a decent size and just shows some yellowing at the bottom, the late nitrogen might do some good,” he said.
The best modes of application are either an aircraft or a highboy rig that allows the producer to dribble the fertilizer between rows.
“It really depends on what equipment you have available,” he said.
Mowrer also noted in his presentation that soil on many Blacklands farms became so badly compacted in the wake of this spring’s heavy rains that nothing the farmers planted came up. He said much of the compaction is caused by working the fields with heavy equipment while the fields are still wet.
“The first pass (with machinery) accounts for 75 to 80 percent of the compaction and other passes compact it even more,” he said. “It’s a good idea to have zones for driving and zones for growing. If you can avoid getting out in the field when it’s wet, you’re better off waiting a couple of days. Waiting won’t affect the compaction as much as getting out in the field when it’s wet.”